PROJECT SUMMARY Recent levels of pertussis in the US are at their highest in 60 years. However, the currently used acellular pertussis vaccine is inadequate and no effective therapies exist for treatment of pertussis. Since antibiotic therapy is ineffective, host-targeted therapeutics are needed. However, we still have a very poor understanding of the pathogenesis of pertussis disease and therefore it is unclear which host targets are appropriate for therapeutic intervention. In RNAseq transcriptomics analysis, we found that the type I interferon (IFN) receptor subunit IFNAR1 was the most significant upstream activator of mouse lung genes differentially expressed in response to Bordetella pertussis infection. Type I IFNs are key cytokines in immune responses and antiviral defense, but they also exacerbate inflammation and pathogenesis in a variety of disease models. Type I IFNs have diverse effects on a variety of bacterial infections, being protective for some and deleterious for others. Our preliminary data suggest that type I IFNs are expressed in the lungs of B. pertussis-infected mice and exacerbate lung inflammatory pathology. We have also been studying sphingosine-1-phosphate (S1P) receptor ligands as candidate host- targeted therapeutics for pertussis. An S1P receptor ligand drug, FTY720, is used in humans as a therapy for relapsing-remitting multiple sclerosis, and other similar drugs are in clinical trials for various inflammatory disorders, demonstrating the translational potential of these drugs. In published studies, we found that administration of a single dose of S1P receptor ligands to B. pertussis-infected mice significantly reduced lung inflammatory pathology. Furthermore, our new preliminary data suggest that S1P receptor ligand treatment reduces inflammation by downregulating type I IFN responses in B. pertussis-infected mice, consistent with the hypothesis that type I IFNs exacerbate lung inflammatory pathology. Therefore, the specific aims of this R21 exploratory/developmental proposal are to test the hypotheses that (i) type I IFNs contribute to lung inflammatory pathology and pathogenesis of B. pertussis disease, and (ii) S1P receptor ligands attenuate lung inflammatory pathology in B. pertussis- infected mice by inhibiting type I IFN signaling. We will use a combination of mouse infection and cell culture studies to test these hypotheses, and we will take advantage of genetically altered mice that impact type I IFN receptor signaling. Identification of host targets and development of novel therapeutics for individuals suffering from debilitating and sometimes fatal pertussis will have a major public health impact on this disease.